1. Field of the Invention
The present invention relates to a method and an apparatus for evaluating a microwave integrated circuit in process of manufacturing and adjusting the circuit within a predetermined standard range.
2. Description of the Related Art
Generally, a microwave integrated circuit includes active devices, such as microwave transistor, passive devices required for operating the active devices, and a microwave circuit having high frequency conductors for connecting them in high frequency, which are integrated on a substrate. In some hybrid type of microwave integrated circuit, a plurality of devices are mounted on a dielectric substrate formed of resin or ceramics with an excellent high frequency characteristics. In another type of microwave integrated circuit, a microwave transistor for semiconductor device is integrated on a single semiconductor substrate with a high frequency circuit, e.g. input or output circuit. This type is referred to as MMIC (monolithic microwave integrated circuit), which can be used for a microwave power amplifier.
The microwave integrated circuit may include an amplifier, a frequency mixer or converter, oscillator, an intermediate frequency circuit, a high frequency wave filter, an antenna circuit, or the like for microwave communications, wherein a microwave transistor for power amplification may be mounted.
In these microwave integrated circuits, laminar devices are layered on the substrate by forming a metal film, a resistive film or a dielectric film using vapor deposition or CVD (chemical vapor deposition), or by partially etching the surface of the device material which has been formed on the substrate using chemical etching or other technique.
For example, a resist pattern having an opening portion at a location for process is formed by applying a photosensitive resist film over the substrate, and patterning in advance the film with a mask having a shape for process using photo lithograph, and developing the film using immersion in a suitable solvent. Subsequently, some processing, such as etching or vapor deposition, are effected on the substrate or another membranous material on the substrate through the opening portion of the resist film.
Particularly, since gold (Au) wiring is effected on a substrate of GaAs system, for example, in process of manufacturing MMIC, Au-wiring using lift-off or ion-beam milling is widely employed to avoid dry etching. Air-bridging technique is also employed if needed for circuit configurations.
An ink injection technique for forming a coat has been already known. For example, the related prior art, Japanese Patent Unexamined Publications (koukai) JP-2003-133692 A, discloses a method for forming a coat, wherein an inkjet nozzle injects a small droplet of paste containing particle powder of an electrically conductive material and solvent onto a substrate or a forming layer on a substrate. This technique can make components and wiring elements in-between of a circuit device to complete the circuit device by discharging a number of droplets from the nozzle, and partially overlapping ink dots on the substrate, and forming a line or a film while adjusting relative movement between the substrate and the inkjet nozzle.
In a microwave integrated circuit, such as MMIC, a transistor is formed on a semiconductor substrate using deposition or lithograph technique as described above, and a capacitor, a resistor, an inductor, a strip line, a connecting line for connecting them, pads for input and output, and the like are also formed on the same substrate using etching, lift-off, or other film forming technique. In process of manufacturing, generally, a number of MMICs are formed on a single semiconductor wafer, and then each of chips is divided out by dicing to be mounted in a package.
A microwave integrated circuit is subject to the evaluation test of high frequency characteristics at a step of a final product or an intermediate step. For example, each of MMIC formed on the semiconductor wafer is subject to the measurement of operation characteristics of a circuit including a transistor, in which a DC probe for the microwave transistor and a high frequency probe for input and output are in contact with input and output ports of the corresponding chip to recognize characteristics of each manufactured product. The results of performance tests on the direct current and high frequency characteristics are used for criteria to examine specifications of the product. All of the ICs rejected by the examination are discarded.
Among the ICs rejected by the characteristics examination at the final product step, there are various ICs including not only defect of the microwave transistor circuit but also other defect of the wiring for the active device and connecting the devices. In many case, the cause of defect is clear, and removing and repairing the defect would allow the rejected ICs to satisfy the specifications of the product.
The other related prior arts are listed as follows:
Web page(http://www.aist.go.jp/aist_j/press_release/pr20020401/pr20020401.html)(2002), and Japanese Patent Unexamined Publications (koukai) JP-2002-134878 A, JP-2002-324966 A, JP-2001-274344 A, JP-2003-86584 A.